1. M.T. Kuhn* and P. M. VanRaden USDA-AIPL, Beltsville, MD
Use of early lactation days open records for genetic evaluation of cow fertility
M.T. Kuhn* and P. M. VanRaden
USDA-AIPL, Beltsville, MD

2. Introduction
- National genetic evaluation for female fertility introduced in February, 2003
- Evaluations are based on Days Open (DO)
- Current requirement:
Records must be a minimum of 250 days in milk

3. Reason for 250 DIM Requirement
- Avoid potential bias
- Sires poor for fertility:
- Only best daughters available early in
lactation
 upward bias for poor sires

4. Consequence of 250 requirement:
- Young bulls:
- First proof for yield 40 days after
daughters initiate first lactation
- Must wait 7 more months for DPR
evaluation

5. Objectives - Develop a predictor for DO
- Determine how early in lactation it can be used

6. ß5*(DO based on last breeding)
Prediction Equation
ŷ = Intercept +
Lactation +
Calving Ease (CE) +
ß1*Age + ß2*Age
ß3*Milk + ß4*Milk2 +
ß5*(DO based on last breeding)
- Models without milk yield also examined

7. Prediction Equation
- Model is fit separately for each of 9 DIM groups:
70, 90, 110, 130, 150, 170, 190, 210, 230
Define:
DO70 = DO based on breedings up to 70 DIM
DO90 = DO based on breedings up to 90 DIM
. .
DO230 = DO based on breedings up to 230 DIM

8. Evaluation of the Predictor
- Bias: Compare ŷ vs y
- Cor(ŷ, y)
- Phenotypic
- Genetic
- Compare: PTAŷ and PTAy

9. DATA - Years available: 1995-1999
3 main things to do:
1) Estimate effects in prediction model, solutions to be used to calculate ŷ’s
2) Estimate genetic correlations
3) Calculate PTAs: PTAy vs PTAŷ
DATA
- Breeding records from 4 DRPCs
- Years available:
- Date of breeding, service sire, service number
recorded for each service on each cow-lactation

10. Estimation of Genetic Correlations
- Vars/Covs estimated using REML
- Model for estimation:
y = HYSP + Sire + e
- 11 traits:
Actual DO, DO70, DO90, …, DO230, Milk
- Data from
  670,000 records, sires

11. Comparing PTAs - Data from 1995-1998  375,000 records
- Only 1998 records were predicted
 127,000 predicted records
- Animal model for calculation of PTAs:
y = HYSP + A + PE + e

12. RESULTS Percentage of cows with a breeding by DIM
Days Percent Cumulative %
>

13. Phenotypic Comparisons
Trait Mean Cor
Actual DO DO DO DO DO DO DO DO DO

14. Genetic Correlations of Predicted and Actual DO
Prediction Model
Day W/ Milk No Milk Mix

15. Genetic Correlations of Predicted DO with Milk
Prediction Model
Day W/ Milk No Milk Mix
Gen Cor of milk with Actual DO = .31

16. Cow PTAs Based on Actual vs Predicted Records
Mean*
DIM PTAŷ-PTAy Corr
*Expressed in standard deviation units
w/ Milk in ŷ
for all records
Milk if no brdg,
No milk, o.w.

17. Sire PTAs Based on Actual vs Predicted Records1
Mean2 Corr Rank
DIM PTAŷ-PTAy (PTAŷ, PTAy) Corr
1 Predictor included milk if no breeding, no milk if with breeding
2 Expressed in standard deviation units

18. Conclusions 1. Projection of DO records will utilize: - Lactation
- Calving ease score
- Age
- DO based on last breeding
- Milk yield, if no breeding
2. Records can begin to be used at 130 DIM
 Reduction of 4 months